Juniper Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Cedar-apple rust | Smooth, round galls on twigs are up to golf ball size. Their surface may be dimpled like a golf ball. | Gymnosporangium juniperi-virginianae | Prune and destroy galls before the spore horns develop. In the nursery, apply azoxystrobin, trifloxystrobin, mancozeb, myclobutanil, propiconazole, triadimefon, or mancozeb + thiophanate methyl in the mid July through August. |
| Cedar-quince rust | Young leaves and twigs have bright-orange spots that look like paint splatters in the spring. These spots darken and become dull orange to rust colored. Slight twig swellings are not obvious except in the spring when their surface is orange with spores. The bark on infected twigs flakes away, growth slows, and twigs die back. | Gymnosporangium clavipes | Prune and destroy galls before the spore horns develop. In the nursery, apply azoxystrobin, trifloxystrobin, mancozeb, myclobutanil, propiconazole, triadimefon, or mancozeb + thiophanate methyl in the mid July through August. |
| Cercospora blight | In the summer, needles become bronzed, tan, and eventually gray. The needles of the inner and lower branches are affected first. The disease progresses upward on the shrub and outward toward the branch tips. This differs from twig blights which start at branch tips. Dark fungal fruiting structures break through the surface of infected needles. Microscopic examination of the spores reveals dark, multicelled spores that are longer than they are wide. Affected branches thin and fall, giving the shrub an open, bare appearance. | Cercospora sequoiae var. juniperi | The fungus overwinters on the plant, spores are present all year, and infection can occur whenever temperatures are mild and moisture is on the needles. Removal of the plant is better than attempting to control this disease with fungicides. However, copper hydroxide, azoxystrobin, tridimefon, mancozeb, or myclobutanil can be used. |
| Kabatina twig blight | Tips of branches die and turn brown or ash gray. These remain on the shrub for many months. Larger branches can be invaded and girdled. On the dead tissue where it meets the still-living wood, small, black, pimple-like fungal fruiting structures form. Microscopic examination reveals oval, colorless spores. See Phomopsis below. | Kabatina juniperi | Prune and destroy infected twigs and branches. It is possible for both Kabatina and Phomopsis twig blight to occur on the same plant. If only Kabatina is present, apply mancozeb. Otherwise, apply mancozeb + thiophanate methyl whenever new growth is present on the shrub. |
Cedar-apple rust galls at dormancy in winter, early telial horn emergence, and full telial horn emergence in the Spring.
Cedar-quince rust gall at a very young stage and an older gall with telial horn emergence.
Twig blight by either Phomopsis or Kabatina . Microscopic examination of the fruiting structures and spores is
required to determine which fungus is involved. Phomoposis produces two spore types in a pycnidium while
Kabatina forms one type of spore in an ascervulus.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Active Ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. no) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| 3 | 2 | Triazole | triadimefon | 12 | Strike (3125-436), Bayleton (432-1360) |
| propaconazole | 24 | Kestrel (66222-41-81943) | |||
| myclobutanil | 24 | Systhane (707-253) | |||
| 11 | 3 | Strobilurin | azoxystrobin | 4 | Heritage (10182-408) |
| trifloxystrobin | 12 | Compass (432-1371) | |||
| M | 1 | Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) |
| manganese + zinc | 24 | Protect T/O (1001-65) | |||
| Combined products | 1 | ||||
| 1 + M | thiophanate methyl + mancozeb | Zyban (58185-31) |
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
DISCLAIMER
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
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